1. Field of the Invention
The present invention relates to an apparatus for producing a metal ribbon and, more particularly, to an apparatus in which a molten metal is poured onto the surface of a roll rotating at a high speed and is then cooled and solidified to form a metal ribbon.
2. Description of the Prior Art
A method has been known in which a metal ribbon is produced directly from a molten metal by pouring a molten metal onto the surface of a roll rotating at a high speed and then rapidly cooling and solidifying the metal to form the metal ribbon.
The apparatus for carrying out this method includes a rotary roll, means for driving the roll and a nozzle for pouring the molten metal onto the outer peripheral surface of the roll. In some cases, a water-cooled roll is used as the rotary roll.
The molten metal discharged from the nozzle is brought into contact with the outer peripheral surface of the roll and rapidly cooled as a result of heat absorption by the roll and is solidified to form a metal ribbon.
At the beginning of the pouring operation, the temperature of the roll surface is sufficiently low to prevent the metal ribbon from being adhered to the roll surface to thereby permit a smooth separation of the ribbon from the roll surface by the centrifugal force generated as the result of the rotation of the roll. However, as the pouring operation is continued, the temperature of the roll surface is gradually increased with a resultant increase in the adhesion of the metal ribbon to the roll surface. Thus, the circumferential distance over which the metal ribbon adheres to the roll surface, i.e., the circumferential distance from the point where the molten metal is poured onto the roll surface to the point where the ribbon leaves the roll surface, is unduly increased until the ribbon extends entirely around the peripheral surface of the roll, with a result that not only the pouring operation cannot be further continued but also the metal ribbon extending around the roll surface breaks the nozzle and/or injures the outer peripheral surface of the roll.
It is, therefore, one of the important problems to be solved in the field of the metal ribbon production that the metal ribbon be prevented from being wound around the roll surface.
In the metal ribbon production of the class discussed, moreover, the ribbon surface which has been solidified in contact with the roll exhibits a state different from that of the ribbon surface which has been solidified without contact with the roll surface. More specifically, innumerable number of minute recesses or depressions are formed in the ribbon surface which has been solidified in contact with the roll surface, to thereby lower the smoothness of the ribbon surface. The recesses are increased in number towards the leading end of the ribbon and are reduced in number towards the trailing end of the ribbon.
The production of a large number of such recesses or depressions considerably deteriorates the lustre of the metal ribbon. In addition, there would be a possibility that these recesses or depressions formed in a metal ribbon may cause a trouble in the mechanical or electrical components made of the ribbon or lower the physical properties of the components. In order to investigate the influence of the recesses or to the physical properties, the inventors have measured the magnetic flux density, the coercive force and other items of ribbons made of a metal consisting of nickel, boron, silicon and the balance consisting of a ferro-alloy. It has been ascertained that the increase in the number of the recesses formed in ribbon surfaces decreases the magnetic flux density but increases the coercive force. This will mean that the magnetic flux density and the coercive force are varied at or in different portions of the metal ribbon in which the density of the recesses varies along the length of the ribbon. In such a case, it will be impossible to obtain mechanical or electrical components of uniform or homogeneous qualities.
Thus, the second problem to be solved in the art is that the metal ribbon surface solidified in contact with a roll surface be freed from the production of recesses to thereby improve the smoothness of that ribbon surface.